The use of colloidal materials for investigating the functionality of the lymphatic system is well known. Radioactive nanocolloids are used in nuclear medicine for bone marrow scanning, inflammation imaging and investigating lymphatic drainage, including the identification of the ‘sentinel node’ in investigations of metastatic spread of some cancers. Only a limited number of commercial products are currently available, including technetium-99m (99mTc) colloidal albumin formulations (eg those sold under the trade names NANOCOLL, in which 95% of the particles have a diameter of ≦80 nm, and ALBURES, in which the mean particle size is stated to be 500 nm) and various sulphur colloids labelled with 99mTc.
It is thought that the differences in particle size and particle size distribution between current formulations are fundamental to the differences exhibited in vivo, eg uptake, biodistribution and clearance. For example, particle size will influence the efficiency with which the particles are engulfed by lymph nodes. Thus, it is desirable for particles with sizes in the sub-micron range (nanoparticles) to be produced with closely defined sizes and size distributions.
It is therefore an object of the invention to provide improved methods for the preparation of nanoparticles having closely defined mean particle sizes and size distributions. Such particles may be useful inter alia for the delivery of therapeutic or other agents to the body, eg when conjugated to a radiopharmaceutical for use in nuclear imaging applications, or to prolong the residence time of proteinaceous material in the body.
It is known that protein particles may be coupled together using so-called zero-length crosslinkers. Such chemistry is disclosed in, for instance, US-A-2005/0036946, which describes the cross-linking of chemically-modified albumin to form solid-like gels. WO-A-00/67774 describes the cross-linking of unspecified mixtures of proteins. Prior to cross-linking the proteins are rendered insoluble and denatured by acidification, addition of non-aqueous solvent and heating to elevated temperature. The product can be recovered by low speed centrifugation and homogenisation is required to allow injection, which indicates that the product is insoluble, with rather large particle sizes. Likewise, WO-A-97/36614 discloses the cross-linking of Protein A at a concentration of 4 mg.mL−1. Similarly, Winkelhake et al, Physiol Chem & Phys 10 (1978), 305-322 describes cross-linking of bovine serum albumin at a concentration of 5 mg.mL−1. The cross-linking of albumin is also described in WO-A-01/45761, the product being used as a sealant, which shows that the product must have the form of a macroscopic solid structure.